图1-1-23所示结构，杆I的内力为下列何值？（）

• A.压力<img src="https://timg.fentiku.com/javaimportItems/7ccedf2d1910465fbfe69efadd4fae23/images/b404c.png" />Ｐ <br/>
• B.拉力<img src="https://timg.fentiku.com/javaimportItems/7ccedf2d1910465fbfe69efadd4fae23/images/b4430.png" />P <br/>
• C.压力<img src="https://timg.fentiku.com/javaimportItems/7ccedf2d1910465fbfe69efadd4fae23/images/b4814.png" />P <br/>
• D.拉力<img src="https://timg.fentiku.com/javaimportItems/7ccedf2d1910465fbfe69efadd4fae23/images/b4d7a.png" />P <br/>

正确答案：A